This invention relates to the use of thermoplastic liners within pipe lines, either initially or as a repair. In the case of new piping, the liner will protect the internal walls from deterioration, and the liner can be replaced from time to time. In the case of deteriorated or damaged piping, the liner will restore the fluid transporting capability of the piping and will prevent further interior deterioration. The use of such a liner for protecting the interior of pipe is taught by Dr. Jacques Laurent in French Patent No. 2,503,622 dated October, 1982 in which he teaches the concept of heat transfer and deformation of previously extruded cylindrical tube of thermoplastic material into U-shape cross-section for insertion into and subsequent reshaping to its original extruded form within pipe as a protective liner. It is a general object of this invention to provide a method and apparatus for the manufacture of the deformed tube product useful as pipe liners of the type disclosed in the Laurent patent.
In its broad sense, this method of manufacturing a deformed tube product involves a first step of extruding a tube cross-section as required for use as a pipe liner, and a second step of deforming the extruded tube into a reduced cross-section for insertion into a pipe as a liner therefor. A feature of this method of manufacturing a tube product is the use of thermoplastic material and its temperature control at the successive stages of formation, during extrusion into its initial and subsequent form, during its deformation, and during its return to ambient usable condition. It is an object of this invention to provide a method and apparatus for the manufacture of pipe liners in continuous deformed lengths which are then subsequently returned to their original unstressed extruded cross-section after insertion into the pipe to be protected thereby. In practice, the liner configuration has an outside diameter equal to or slightly greater than the inside diameter of the pipe to be protected, whereby the said liner is either unstressed or under slight circumferential compression; either of which conditions is readily accommodated by the plastic liner which relies upon the surrounding pipe for its structural support.
The first step of this process, that is the extrusion of a tubular cross-section, is state-of-the-art. However, the second step of this process, that is the deformation of the extruded tube into a reduced cross-section, is novel. It is an object of this invention to deform an initially extruded tubular cross-section without adverse effect on its structural integrity, and in such a manner that its initially extruded tubular cross-section can be restored. To this end, controlled heat is applied to establish a softened condition of the thermoplastic material after its extrusion, while simultaneously applying deforming tools thereto in order to reduce its cross-sectional configuration. When the desired reduction is achieved, heat is withdrawn from what is the finished product of continuous length that is then stored on spools for storage, transport and subsequent installation.
This invention is particularly concerned with the second broad step referred to above, which broad step is reduced into smaller secondary steps, so to speak. The following disclosure will concentrate primarily upon these smaller steps with respect to the method and apparatus provided herein to perform said steps and their functions. For example, a U-shaped reduced tubular configuration is shown and described. However, it is to be understood that a V-shaped reduced tubular configuration is essentially the same as the U-shape, except for its acute angle as distinguished from roundness. Also, it is to be understood that other cross-sectional reductions are essentially the same, whether they be H-shaped or X-shaped, or the like; the H-shape being two U's round to round, and the X-shape being four V's angle to angle. The U-shape, or V-shape, is presently considered to be the most practical and preferred configuration for such a tube product.
In carrying out this invention, the deformation of the initially extruded tube, preferably of cylinder form, progresses in a gradual manner, by shaping means. That is, at least one side of the tubular extrusion is increasingly depressed so as to condition the tubular extrusion for its lateral collapse into a reduced U-shaped, or V-shaped, cross-sectional form; thus providing a deformed tube. As pointed out above, the aforesaid deformation is conducted in the presence of controlled heat substantially below fluidity of the thermoplastic material and such that such plastic is deformed without adversely affecting its structural integrity, whether in its deformed condition or in its subsequently re-established initial condition. It is an object of this invention to provide shaping means, preferably in the form of rollers, to deform the initially extruded tube as stated. In practice, the deformation is gradual, step-by-step, utilizing combined pairs of opposed shaping rollers. A feature is the lateral collapse of the tubular extrusion over a forming rail, by means of opposed shaping rollers that embrace such forming rail. The finished product is then cooled to ambient temperature during and/or upon its delivery from the forming rail, as by means of a cooling trough. Heating and cooling is by means of heat absorption or radiant heating, and preferably by temperature controlled water baths or spray.
The present-day commercial demand for this pipe liner is a product ranging from 2 inches to 24 inches in diameter. The wall thickness will vary in proportion to diameter as circumstances require, depending upon the application involving internal pressure applied in use and strength required thereby. Accordingly, there will be variations in the process steps involving the plurality of shaping means disclosed herein as shaping rollers and back-up roller, whereby at least one side of the tubular extrusion is deformed as required. That is, the number of shaping means and the step-by-step degree of deformation is variable, depending upon the size and wall thickness and material to be deformed. A feature of this method and apparatus is that the product is pulled out of the extruder and from the deforming tool, for delivery to a storage spool, in a controlled manner, whereby the cross-sectional configuration of the deformed tube product is uniform and within specified dimensional tolerance. With respect to variations in size and tolerances, and especially with respect to larger diameter pipe liners, it is an object of this invention to provide pulling traction on the tube during its process of deformation, and applied to the shaping means, disclosed herein as powered rollers. In practice, torque is independently applied to the shaping and back-up rollers, so as to ensure uniform advance of the deforming tube product.
The product herein disclosed is a thermoplastic pipe liner that is reduced from its initially extruded cross-section so that it can be easily pulled inside a pipe line and then restored to its initially extruded cross-section. Assuming pipe to be round in cross-section, the outside diameter of the initially extruded and/or reformed liner tube is the same or slightly greater than the inside diameter of the pipe that receives it, so that the liner exterior comes into perfect interface contact with the pipe interior and preferably under slight circumferential compression. This interface contact of liner within the pipe eliminates any annulus, and so that the requirement of filling such an annulus is virtually eliminated. A feature of this liner is its thin-wall configuration made of a thermoplastic such as polyethylene, nylon, Teflon.TM., ABS, or any other such plastic material, whereby the small loss of inside diameter of the flow passage is largely compensated for by the exceptional flow coefficient within the liner made of such a thermoplastic material. For new pipe line projects, extensive pipe materials such as stainless alloys can be substituted with ordinary steel pipe, and lined with this product liner, thereby realizing a cost saving of 1.5 to 2.2, together with the improved fluid tolerance properties of the plastic which can be selected to best advantage. Accordingly, pipe lines which are structurally sound need not be replaced, since this product liner can be installed and replaced as circumstances require.
The method and apparatus herein disclosed for the manufacture of this product liner involves the primary step of extruding thermoplastic tubing, and the secondary step of deforming the thermoplastic tubing. The primary step of extrusion involves generally, an extruder that receives raw plastic material and delivers a tubular cross-section through a vacuum trough that controls the processing temperature and precise configuration of the tubular cross-section. The secondary step of deforming the precise tubular cross-section involves generally, a multi-stage shaping tool that deforms the extrusion at controlled temperature and delivers it through a cooling trough as the finished product liner. The finished product liner is drawn from the secondary step by a puller that controls the linear speed of the production and maintains a constant wall thickness of the finished product liner.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.